While connecting wattmeter the terminals M and C should be connected. This leads to the wrong measurement of power consumed by load ZL. Hence, the wattmeter should always be connected as shown in the figure. Experiment no. Also, sometimes in a new installation, two units in parallel, though more expensive, may be preferred over a single unit for the reasons of reliability- half the load can be supplied with one unit out.
Further, the cost of maintaining a spare is less with two units in parallel. The satisfactory and successful operation of transformers connected in parallel on both sides requires that they fulfill the following conditions: 1. The transformers must be connected properly as far as their polarities are concerned so that the net voltage around the local loop is zero.
A wrong polarity connection results in a dead short circuit. The secondary sides of the two-single phase transformers must have zero relative phase displacement. The transformer must have the same voltage ratings to avoid no-load circulating current. Since the leakage impedance is low, even a small voltage difference can give rise to considerable no- load circulating current and extra I2R loss. All the quantities are referred to the primary side.
Objectives: 1. To determine and verify the polarity of the individual single-phase transformers. To find the impedance of the single phase transformers by short circuit test. To study parallel operation of the above two single phase transformers and observe the load sharing between them. Determination of Polarity of a Single Phase Transformer: 1. Mark the primary winding terminals of one single phase terminals as A1 and A2. The choice of terminal for marking is arbitrary. Similarly mark secondary winding terminals as a1 and a2.
Connect the terminals of the two windings as shown in Fig. Also connect the primary winding terminals to an autotransformer through a double pole double throw DPDT switch Fig. Make sure that the autotransformer is in the zero voltage position. Now switch on the power supply and throw on the DPST switch.
Gradually increase the autotransformer voltage up to the rated primary voltage and measure the voltage between terminals A2 primary and a2 secondary from voltmeter V. Suppose the rated voltage ratio of the transformer is V1:V2. Turn off the power supply. Determine the polarity of the other transformer following the same procedure. Switch on the power supply to the autotransformer and follow the same procedure as before while gradually increasing the autotransformer output voltage keeping S1 closed.
The Wattmeter connections should be made as was explained earlier in the manual. Observe the reading of V2. In case polarity reversal is to be made switch off the system following the procedure mentioned above, and change the connections of any one transformer i. Having done the polarity check next close the switch S2. For the load choose a gang rheostat of appropriate power rating If the transformers are perfectly matched or are near perfectly matched, as is the requirement for zero inter transformer circulation current, the power sharing will be in accordance with the respective power ratings of the two transformers.
All autotransformers are normally made in implementing open with a degree of protection IP00 or IP20 request. The voltage drops vacuum charged are contained, which can be available in high output power of short duration of opportunity needed for the operation of the apparatus of command. In the case of cyclic operation, however, if you use the full strength reported in the tables is necessary to limit the frequency of a drive maneuvers per hour to meet the value of overtemperature admitted.
Use the appropriate cables according to the current game and the capacity of the terminals. In addition to special care not to tighten the insulating sheaths under the terminal screws.
In fact, a bad contact can lead to localized heating that can lead to damage to components. The installation and replacement of transformers is to be performed by qualified persons..
Single phase autotransformer Assembly instructions IVA e C. Designed by Digicolor.
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